Abstracts

Rationale: Focal Cortical Dysplasia (FCD) is the most common etiology found in surgical series of pediatric epilepsies. Incorporating FDG-PET/MRI coregistration in the presurgical evaluation improved the detection of FCDs. However, there is a subtype of FCD Type IIA/B, which is subtle on MRI and difficult to detect on FDG-PET.Methods: We retrospectively reviewed 22 patients (mean age 14.5y, sd=3.1) with histopathology proven FCD Type IIA/B in the frontal lobe. Two neuroradiology fellows, who were blinded to the known locations of FCDs evaluated preoperative FDG-PET/MRI coregistration images to identify the zone of hypometabolism. Locations of FCDs were subdivided into three groups: 1, Lateral/Opercular Frontal, 2, Superomedial Frontal; and 3, Orbital Frontal. The degree of FDG-PET hypometabolism was separately measured using the lesion’s median standard uptake value (SUV) related to the basal ganglia (SUV ratio), which was used as a reference.Results: Raters were able to identify 80% of lateral frontal (n=10) and 80% of orbital frontal (n=5) FCDs. For superomedial frontal FCD (n=7) only 28.6% was detected. The lesions in the superomedial frontal lobe had a significantly less hypometabolism (SUV ratio >0.56). Raters were able to identify the FCDs only when SUV ratio was lower than 0.56.Conclusions: Subtle FCD TypeIIA/B located in the superomedial frontal lobe and with SUV ratio over 0.56 showed false negative results on FDG-PET/MRI coregistration. Understanding this pitfall will be important for presurgical epilepsy evaluation and will require a different approach using other modalities in these pediatric epilepsy patients.